1. Field of the Invention
The present invention relates to a sintered alloy composition and a manufacturing method thereof, and more particularly to a sintered alloy composition having excellent abrasion and corrosion resistance, preferably to be used for making machine parts such as valve seats for engines.
2. Description of the Prior Art
Most machine parts such as valve seats for internal combustion engines are required to have mechanical strength and resistance. For example, in the case of a valve seat of an internal combustion engine, a valve reciprocates at high speed and experiences slight pivotal motion during engine operation, and the valve seat receives the reciprocating valve on its seat surface. Consequently, the valve seat suffers continuous impacts from the valve while being exposed to hot combustion gas produced in the engine cylinder. Therefore, it is of course important for the valve seat of the engine to have abrasion resistance. Moreover, with regards to structure, the valve seat is fitted to the cylinder head of the engine only by inserting it with pressure into a fitting hole in the cylinder head. According to this structure, if the valve seat has poor radial crushing strength, trouble can arise that will cause the valve seat to get loose and fall out of the fitting hole. In view of the above, it is also important for the valve seat of the engine to have sufficient hardness and strength (radial crushing strength).
In internal combustion engines for motorcars, valve seats had at first been manufactured by using cast iron alloy. At present, they are manufactured with sintered iron alloys. However, such iron alloy are not suitable for machine parts such as a valve seats for outboard engines for marine vessels, because those machine parts are utilized in highly corrosive environments where they are in contact with sea water and dew arising in salty air.
For this reason, in the manufacturing of outboard engines, aluminum bronze has conventionally been employed as a material for the valve seat. However, in accordance with recent trends for a high-power outboard engines, structural parts of outboard engines need to have vastly improved mechanical properties. Accordingly, the material for valve seats also has to have better mechanical properties such as abrasion and corrosion resistance.